CRASH BOX --made from a metal Christmas popcorn container.
Fill it with junk , but not glass. Roll it around in all directions
for a variiety of sounds.

OLD DIAL TELEPHONE - and ringer bell box -- the kind companies use
for delivery doorbells. Don't bother trying to make the old phone ring--it'll
cost hundreds for a step down transformer to deliver the 84 volts necessary
to engage the phone ring circuit. Just build a $10 ringer box. (See the "advanced
SFX" listing below).

VIBRO PEN - A "Dizzy Doodler" pen that writes wobbly--for
planes/jackhammers. Turn it on and apply the top (not the pen) to a cardboard
box for a convincing airplane. Do the same on a stack of saucers and you'll
have a great jack-hammer.
The KB Toy liquidator chain sells them for $4.

TOY CELL-PHONE - For radars, space beeps, even cell-phones!

SLIDE WHISTLE - Besides eeeeeYOOOP, it can also be quickly slid back
and forth for radars and space sounds.

PLASTIC EGG MARACAS - for jungles, rattlesnakes, weirdness.
You could make some with plastic easter eggs and rice, but many music stores
sell them.